Various types of conveyors are available which each employ an elongate, slightly downwardly inclined tray or pan having a planar surface for transporting goods thereon. These types of conveyors are preferred in various industries since the goods being transported along the tray need only engage a unitary tray during the conveying operation, and since the tray may be easily cleaned. Conveyors of this type have been used for decades and include those commonly referred to as reciprocating conveyors, shaker conveyors, or vibratory conveyors.
Differential impulse conveyors may also use a slightly downwardly inclined tray, but alternatively may use a horizontal tray or slightly upwardly inclined tray. Differential impulse conveyors, which are sometimes referred to as linear motion conveyors, are operationally distinguishable from vibratory conveyors because the tray is moved slowly forward to convey the goods with respect to the tray, and then is moved rearward at a high return speed so that the goods slide along the tray, thereby effectively transporting the goods along the conveyor tray. A significant advantage of differential impulse conveyors is that these conveyors do not tend to damage fragile goods. Moreover, a differential impulse conveyor does not require gravity to move goods along the tray, and accordingly the tray supporting surface may be horizontal or may even be inclined upwardly. Accordingly, differential impulse conveyors have gained increased acceptance in recent years.
The drive mechanism for a differential impulse conveyor generates repeated acceleration and deceleration of the tray. Since the forward acceleration is less than the rearward acceleration, the goods move with the tray when the tray moves forward, and slide with respect to the tray when the tray moves rearward. Early types of drive mechanisms for achieving this motion in a differential impulse conveyor included a plurality of weights which were moved back and forth to obtain the desired movement of the tray. These inertia drive systems impart high loads to the conveyor support structure or base, and thus typically require a heavy and expensive support structure for the conveyor. These inertia drive systems undesirably require a fair amount of startup time before the motor driving the weights causes the tray to move in its desired manner, and similarly result in tray movement for a period of time after the drive motor is de-energized. Also, these inertia drive mechanisms are costly and complicated, and frequently have high maintenance costs.
Another type of drive mechanism for powering a differential impulse conveyor utilizes a power source which cooperates with mechanical components which directly move the tray. One such arrangement, as disclosed in U.S. Pat. No. 5,351,807, employs an angled universal drive and a speed reducer to achieve the desired tray movement. Other drive systems for powering a differential impulse conveyor are disclosed in U.S. Pat. No. 5,794,757. One drive mechanism recently introduced to the marketplace employs a plurality of eccentrically mounted pulleys. A crank arm interconnects one of the pulleys and a tray support arm to drive the conveyor tray slowly forward and then quickly backward. The systems disclosed in the above two patents have significant advantages over inertia drive systems for powering a differential impulse conveyor. These drive systems have the ability to substantially instantaneously achieve the desired tray motion when the drive unit is started, and similarly instantaneously stop the tray motion when the drive unit is stopped. This is a significant advantage of these drive units compared to the inertia drive mechanisms, and allows the differential impulse conveyor to be reliably used for cross-feed applications. The size and expense of these latter described drive systems, as well as the number of moving parts, nevertheless restricts the acceptability of differential impulse conveyors, particularly in applications wherein the size and cost of the drive system are significant factors to the customer.
The disadvantages of the prior art are overcome by the present invention. An improved differential impulse conveyor with a linear drive mechanism is hereinafter disclosed. The drive mechanism has few moving parts, and in many applications requires less space and cost than other drive mechanisms. An improved connector is also disclosed for pivotally interconnecting a stationary member and a member movable with respect to the stationary member such that the movable member reciprocates in a straight line path rather than in an arcuate path.